Inheritance in C#. Abstract class. Polymorphism презентация

AGENDA
Implementation inheritance
Abstract class
Virtual methods
Sealed classes and methods

TYPES OF INHERITANCE
Implementation inheritance means that a type derives from a base type, taking all the base type’s member fields and functions.
Interface inheritance means that a type inherits only the signatures of the functions and does not inherit any implementations.

IMPLEMENTATION INHERITANCE
Inheritance enables us to create new classes that reuse, extend, and modify the behavior that is defined in other classes.
The class whose members are inherited is called the base class, and the class that inherits those members is called the derived class.
The idea of inheritance implements the IS-A relationship.
Animal
Dog
Shape
Circle
Doctor
Cardiology
class Animal {…}
class Dog: Animal
{ …}
class Shape{…}
class Circle: Shape
{ …}
class Doctor{…}
class Cardiology: Doctor
{ …}

IMPLEMENTATION INHERITANCE
A derived class can have only one direct base class.
Inheritance is transitive. If ClassC is derived from ClassB, and ClassB is derived from ClassA, ClassC inherits the members declared in ClassB and ClassA.
Person
Student
Staff
Developer
Teacher

EXAMPLE

THE base keyword IS USED TO ACCESS MEMBERS OF THE BASE CLASS FROM WITH IN A DERIVED CLASS

ABSTRACT CLASS
An abstract class cannot be instantiated.
The purpose of an abstract class is to provide a common definition of a base class that multiple derived classes can share.
Abstract classes may define abstract methods.
Derived classes of the abstract class must implement all abstract methods.

EXAMPLE

INTERFACE vs ABSTRACT CLASS
What is the difference between an abstract class and an interface?
An abstract class can have fields and implementation of methods.
An abstract class is essentially the same thing as an interface except it is an actual class, not just a contract.
abstract classes with virtual methods have better performance than interface implementation
Car
Plane
Boat
Labrador
Husky
German Shepherd Dog
Implements
Extends
Vehicles
Dog
Interface
Abstraction

INTERFACE vs ABSTRACT CLASS

VIRTUAL METHODS
Virtual method - a method that can be overridden in a derived class.
Overriding method - a change of its implementation in derived classes.
Static method can not be virtual

VIRTUAL AND ABSTRACT METHODS
Abstract method is a method that does not have its implementation in the base class, and it should be implemented in the derived class. Abstract method can be declared only in abstract class.
What is the difference between the virtual and the abstract method?
The virtual method can have its implementation in the base class, abstract - no (body is empty);
An abstract method must be implemented in the derived class, the virtual method is not necessary to override.
Announcement of the abstract method:
[модифікатор доступу] abstract [тип] [ім'я методу] ([аргументи]);
The implementation of the abstract method in the derived class occurs in the same way as the override of the method - using the keyword override:
[модифікатор доступу] override [тип] [ім'я методу] ([аргументи])
{
// Реалізація методу
}

ABSTRACT PROPERTIES
Creating abstract properties is not very different from the methods:
Realization in the derived class:
protected [тип] [поле, яким управляє властивість];
[модифікатор доступу] abstract [тип] [ім'я властивості]{get; set;}
[модифікатор доступу] override [тип] [ім'я властивості]
{
get {тіло аксессор get}
set {тіло аксессор set}
}

EXAMPLE

EXAMPLE

TASK 8
1. Add two classes Persons and Staff (use the presentation code)
2. Create two classes Teacher and Developer, derived from Staff.
Add field subject for class Teacher;
Add field level for class Developer;
override method Print for both classes.
3. In Main, specify a list of Person type and add objects of each type to it. Call for each item in the list method Print ().
4. Enter the person's name. If this name present in list - print information about this person
5. Sort list by name, output to file
6. Create a list of Employees and move only workers there. Sort them by salary.